Food establishments such as grocery stores and fast-food establishments often utilize food warmers to maintain prepared food at a constant predefined temperature. These establishments are required by law to keep such food items at the predefined temperature. For example, health and safety regulatory agencies mandate that perishable meat items be maintained at or above 140 degrees F. The food warmers typically have a warming plate enclosed by a support structure. The support structure has a door or other opening for access to the warmer. Employees or customers are allowed to take food items from the food warmer as desired.
However, conventional food warming equipment and hot merchandising equipment have proven unsatisfactory in maintaining food at the required temperature under certain conditions. In some instances, there is no feedback of the current temperature of the food warmer, i.e., no feedback between the heat applied and the heat extracted (by the food and environment) from the food warmer. Heating elements in those instances merely supply a constant power input to keep the food warmer enclosure at an expected resulting temperature. However, environmental effects such as the ambient room temperature, actual voltage of the power supply, and manufacturing tolerances of the electrical elements will effect the actual temperature at which the food is maintained. The ambient room temperature effects are increased by persons opening the food warmer to retrieve or replace food items in the food warmer. Additionally, when unheated food items are placed in the food warmer, the lack of feedback will allow the overall temperature of the food warmer to decrease due to conductive heat transfer between the warmer and the food item. This will, in turn, cause the temperature of other food items being heated by the warmer to decrease below the required temperature.
To combat this problem, food warmers employing a feed back device, such as a thermostat, have also been employed. A problem with these food warmers is that the single thermostat cannot detect temperature variances across the food warmer. Temperature variances are introduced in the food warmer by air drafts at ambient temperature or being placed adjacent to refrigeration units, as well as by placing unheated food items on the food warmer. Because the thermostat will only detect the temperature of the food warmer at one location, a decrease in temperature of a section of the food warmer remote from the thermostat will not be detected. Likewise, if the section of the food warmer near the thermostat decreases in temperature, the thermostat reacts by supplying energy to the heating elements over the entire food warmer, thereby overheating remote sections of the food warmer. Thus, food items can be overheated to compensate for inadequate heating in other areas of the food warmer.
U.S. Pat. No. 5,590,587 to Polster ("Polster") discloses a food cooker/rethermalizer wherein food items are heated in a water bath. Polster uses two thermostats 81a and 81'a to sense the temperature of the water bath within a water compartment divided into zones A, B, C. Based on the average temperature sensed by the thermostats 81a, 81'a, a heater 80 is supplied or not supplied energy to maintain a desired temperature of the water bath. Polster, however, cannot sense for temperature variances across the water bath. Rather, Polster anticipates a temperature variance by using the average temperature of the water bath at two locations to control the heating element. Also, by placing only one heating element 80 in the food cooker/rethermalizer, disposed at one end of the water compartments A, B, C, Polster does not attempt to eliminate any temperature variance within the compartments A, B, C.
The present invention is provided to solve these and other problems.